Conventionally, audio or video information is digitized for easy treatment in a personal computer, various mobile electronic devices or the like. Namely, digital data can easily be recorded, reproduced or transmitted without being deteriorated in quality. Such digital audio or video information can have its frequency band compressed with the audio and video codec techniques for easier and more efficient distribution to a variety of communication terminals via digital communication and broadcasting. For example, audio and video data (AV data) can be received by a mobile phone out of doors.
Recently, transmission/reception systems for such digital information are practically used in various manners since there have been proposed network systems suitable for outdoor use as well as for use in a small-scale area. As such network systems, there have been proposed, in addition to a week radio-wave system using a frequency band of 400 MHz and personal handy-phone system (PHS) using a frequency band of 1.9 GHz, various types of next-generation radio communication systems including a radio LAN system using a frequency band of 2.45 GHz and small-scale radio communication system called “Bluetooth”, both proposed in IEEE 802.11b, and a narrow-band radio communication system using a frequency band of 5 GHz proposed in IEEE 802.11a. With the effective use of such various radio communication system and also various types of communication terminals, the digital information transmission/reception systems can transfer and receive various kinds of data by various types of communication terminals in various places, for example, in doors, out of doors or the like, access a communication network such as the Internet, and transmit and make data transmission and reception to and from the communication network. However, the above data communications can be done easily, not via any repeater or the like.
For the digital information transmission/reception systems, however, the communication terminal having the above communication functions should essentially be compact and lightweight, and portable. Since the communication terminal has to modulate and demodulate analog high-frequency signals in a transmission/reception block thereof, so it generally includes a high-frequency transmission/reception circuit of a superheterodyne type designed to convert the signal frequency into an intermediate frequency once for transmission or reception.
The high-frequency transmission/reception circuit includes an antenna block having an antenna and a select switch and which receives or transmits information signals, and a transmission/reception selector which makes a selection between transmission and reception modes of operation. The high-frequency transmission/reception circuit also includes a reception circuit block composed of a frequency convert circuit, demodulation circuit, etc. The high-frequency transmission/reception circuit further includes a transmission circuit block composed of a power amplifier, drive amplifier, modulation circuit, etc. The high-frequency transmission/reception circuit also includes a reference frequency generation circuit block which supplies a reference frequency to the reception and transmission circuit blocks.
The above-mentioned high-frequency transmission/reception circuit is composed of many parts including large functional components such as various filters interposed between stages, local oscillator (VCO), surface acoustic wave (SAW) filter and the like, and passive components such as an inductor, capacitor, resistor and the like provided peculiarly to high-frequency analog circuits like a matching circuit, bias circuit, etc. In the high-frequency transmission/reception circuit, each of the circuit blocks is implemented in IC-chip form. However, since each of the filters interposed between the stages cannot be assembled in any IC, the matching circuit has to be provided as an external device for the high-frequency transmission/reception circuit. Therefore, the high-frequency transmission/reception circuit as a whole is so large that the communication terminal cannot be designed compact and lightweight.
On the other hand, some communication terminals use a direct conversion-type high-frequency transmission/reception circuit which transmits and receives information signals without conversion of the signal frequency into an intermediate frequency. In this high-frequency transmission/reception circuit, information signals received by the antenna block are supplied through the transmission/reception selector to the demodulation circuit where they will undergo a direct baseband processing. In the high-frequency transmission/reception circuit, information signals generated by a source have the frequency thereof not converted once by the modulation circuit into any intermediate frequency but modulated directly to a predetermined frequency band, and sent from the antenna block via the amplifier and transmission/reception selector.
Since the above high-frequency transmission/reception circuit is constructed to transmit and receive information signals with the direction modulation of the signal frequency but without conversion of the signal frequency into any intermediate frequency, it can be composed of a reduced number of parts such as the filter etc. so simply as to have a generally one-chip construction. Also, in the high-frequency transmission/reception circuit of the direct conversion type, something has to be done about the filter or matching circuit provided in the downstream stage. In the high-frequency transmission/reception circuit, since signals are amplified once in the high-frequency stage, so it is difficult to make a sufficient gain. Therefore, it is necessary to make amplification of the signals in the baseband processing block as well. Therefore, a DC offset cancel circuit and an extra lowpass filter have to be provided in the high-frequency transmission/reception circuit, which will lead to a larger total power consumption.
The conventional high-frequency transmission/reception circuit, whether of the aforementioned superheterodyne type or of the direct conversion type, does not meet the requirements for the compact and lightweight design of the communication terminals. On this account, various approaches have been made to design a more compact and lightweight high-frequency transmission/reception circuit by designing a simple-construction high-frequency transmission/reception module with the Si-CMOS technique, for example. In a typical example of such approaches, the high-frequency module is built in a one-chip form by forming passive elements each having a good performance on an Si substrate while forming a filter circuit and resonator in an LSI and integrating an logic LSI for the baseband processing circuit. Since the Si substrate is electrically conductive, however, it is difficult to form an inductor and capacitor each having a high Q value on the main side of the Si substrate. In this case, such approaches essentially depend upon how higher-performance passive elements are formed on the Si substrate.
FIGS. 1A and 1B show together a conventional high-frequency module. The high-frequency module is generally indicated with a reference 100. It includes a silicon substrate 101, SiO2 insulative layer 102, first wiring layer 105, second wiring layer 106 and an inductor 107. The assembly of the silicon substrate 101 and SiO2 insulative layer 102 has formed therein a large concavity 104 which defines a place (indicated at a reference 103) where the inductor 107 is to be formed. The first wiring layer 105 is formed in the concavity 104. The second wiring layer 106 is formed on the top of the silicon layer 101 and the inductor 107 itself is provided over the concavity 104. Since the inductor 107 faces the concavity 104 and is supported by the second wiring layer 106 in air over the concavity 103, so its electrical interference with the circuit inside via the silicon substrate 101 is smaller, and thus the high-frequency module 100 has an improved performance. However, the inductor 107 included in this high-frequency module 100 is formed through many difficult processes and with an increased manufacturing cost.
FIG. 2 shows a conventional silicon substrate. As shown, the silicon substrate, generally indicated with a reference 110, includes a silicon substrate 111, SiO2 layer 112 formed on the silicon substrate 111, and a passive element forming layer 113 formed on the SiO2 layer 111 by the photolithography. The high-frequency module 110 has passive elements such as an inductor, capacitor or resistor formed in multiple layers, each along with a wiring element, in the passive element forming layer 113 with the thin and thick film technologies, which will not be described in detail herein. In the high-frequency module 110, the passive element forming layer 113 has viaholes 114 formed appropriately therethrough to provide an interlayer connection and a terminal 115 formed on the surface layer thereof. A chip 116 such as a high-frequency IC, LSI or the like is mounted on the high-frequency module 110 on contact with the terminal 115 by the flip chip bonding or the like to form a high-frequency circuit.
Such a high-frequency module 110 is mounted on an interposer circuit board or the like having a base-band processing circuit and the like formed thereon to make an isolation between the passive element forming layer and base-band processing circuit by means of the silicon layer 111, thereby permitting to suppress an electric interference between the passive element forming layer and base-band processing circuit. Since the silicon layer 111 is electrically conductive, the high-frequency module 110 can effectively function when a high-precision passive element is formed in the passive element forming layer 113. On the other hand, however, the silicon layer 111 being electrically conductive will inhibit each of passive elements from a having good high-frequency performance.
FIG. 3 shows another conventional high-frequency module. The high-frequency module, generally indicated with a reference 120, uses a substrate 121 not electrically conductive such as a glass substrate or ceramic substrate to solve the problems of the aforementioned silicon substrate 111. As shown, this high-frequency module 120 includes a substrate 121 and a passive element forming layer 122 formed on the substrate 121 by photolithography. Similarly to the aforementioned conventional high-frequency module 110, the high-frequency module 120 has passive elements such as an inductor, capacitor or resistor formed in multiple layers, along with a wiring element, in the passive element forming layer 122 with the thin and thick film technologies, which will not be described in detail herein. In the high-frequency module 120, the passive element forming layer 122 has a viahole 123 formed appropriately therethrough for an interlayer connection, and a terminal 124 formed on the surface layer thereof. A high-frequency IC 125, chip-shaped part 126 and the like are mounted on the high-frequency module 120 with the terminal 124 laid between them by the flip chip bonding or the like to form a high-frequency circuit.
In the high-frequency module 120 shown in FIG. 3, since use of the substrate 121 not electrically conductive permits to suppress the capacitive coupling between the substrate 121 itself and passive element forming layer 122, a passive element having a good high-frequency performance can be formed in the passive element forming layer 122. In case the high-frequency module 120 is formed from a glass substrate, however, it is difficult because of the characteristic of the glass substrate to form, on the substrate 121 itself, terminals by which the high-frequency module 120 is connected to an interposer substrate 127, for example, when it is mounted on the latter. On this account, in the high-frequency module 120, a terminal pattern 128 is appropriately formed on the surface of the passive element forming layer 122, and the terminal pattern 128 and a terminal pattern 129 appropriately formed at the interposer substrate 127 are connected to each other by a wire 130 with the wire bonding technique or the like, as shown in FIG. 4. It should be noted that the interposer substrate 127 has appropriately formed on the bottom thereof an input/output terminal 131 connected to the terminal pattern 128 through viaholes (not shown).
The above high-frequency module 120 is not advantageous in that the terminal patterns 128 and 129 have to be formed and connected by wire bonding to each other, which will increase the cost of manufacturing and make it difficult to attain a more compact module design. It should be noted that the high-frequency module 120 is packaged with the terminal patterns 128 and 129 or the wire 130 being sealed along with high-frequency IC 125 and chip-shaped part 126 in an insulative resin 132.
On the other hand, in case the high-frequency module 120 is formed from a ceramic substrate, it functions as a package board on no contact with any mother board because a base ceramic substrate can be formed in multiple layers. Since the ceramic substrate is formed from sintered ceramic particles, however, it will have, on a surface thereof where the passive element forming layer 122 is formed, a roughness as large as the ceramic particle size of about 2 to 10 μm. Therefore, to form high-precision passive elements in the high-frequency module 120, the ceramic layer surface has to be flattened by polishing before forming the passive element forming layer 122. Also, since the ceramic substrate has a relatively high specific inductive capacity (8 to 10 in case the ceramic substrate is of alumina, and 5 to 6 in case it is of glass ceramic) while it is low in loss, so the high-frequency module 120 will incur interference between multiple layers of wiring, be lower in reliability and less immune to noises.
To solve the problems of the aforementioned conventional high-frequency modules, the Applicant of the present invention proposed another high-frequency module as shown in FIG. 5. The high-frequency module, generally indicated with a reference 140, includes a base substrate block 141 and a block in which elements are formed (will be referred to as “elements block” hereunder) 142 stacked on the base substrate block 141. The base substrate block 141 is formed from first and second organic substrates 143 and 144 each low in loss because of their low specific inductive capacity and dielectric dissipation factor (Tan δ), and the first and second organic substrates 143 and 144 are bonded integrally to each other with a prepreg 145.
The first and second organic substrates 143 and 144 are formed from a material having the aforementioned characteristics, selected from among organic materials including liquid crystal polymer, benzocyclobutene, polymide, polynorbornen, polyphenylether, polytetrafluoroethylene, bismaleimide-triazine (BT-resin) and any one of these resins having ceramic powder dispersed therein, with the material being integrated with woven glass fabrics 146a and 146b each as a core to assure an improved bending strength, rupture strength, etc.
The base substrate block 141 has a wiring layer formed, with the printed-circuit board technique, on the main side, top or bottom, of each of the first and second organic substrates 143 and 144 to form first to fourth wiring layers 147 to 150. Of the base substrate block 141, the first to fourth wiring layers 147 to 150 are interlayer-connected to each other through viaholes 151 appropriately formed through the layers 147 to 150. The first and second wiring layers 147 and 148 are formed on the top and bottom main sides, respectively, of the first organic substrate 143, while the third and fourth wiring layers 149 and 150 are formed on the top and bottom sides, respectively, of the second organic substrate 144. The high-frequency module 140 has formed inside the base substrate block 141 thereof line patterns 152a and 152b each formed from a distributed parameter circuit including a resonator, filter, etc. or a power circuit, bias circuit, etc. which will not be described in detail.
The high-frequency module 140 shown in FIG. 5 has a passive element 153, inductor 154, passive element 155 or the like formed in the elements block 142 with the thin film technology. In the high-frequency module 140, a high-frequency IC 156 is mounted on the surface of the element forming layer 142 by the flip chip bonding. To efficiently form the line patterns 152a and 152b, power circuit or bias circuit formed in the base substrate block 141 and the passive elements 153 to 155 formed in the element forming layer 142 as above and avoid interference between the elements, the high-frequency module 140 has the first and third wiring layers 147 and 149 formed each as a grounding layer.
Note that the high-frequency module 140 shown in FIG. 5 is packaged with the wiring pattern formed on the surface of the elements block 142 being covered with a protective layer 157 while the high-frequency module 140 and a high-frequency IC 156 are wholly covered with an insulative resin layer (not shown). The high-frequency module 140 has a plurality of terminal blocks 158 formed in the fourth wiring layer 150, and mounted on an interposer (not shown) with the terminal blocks 158 being positioned between them.
The high-frequency module 140 shown in FIG. 5 is characterized in that since the first and second organic substrates 143 and 144 are formed from a relatively low-cost material, the module 140 itself can be produced with a reduced cost and that the desired first to fourth wiring layers 147 to 150 can be formed more easily with the printed-circuit board technique. By flattening the surface of the base substrate block 141 by polishing, for example, the high-frequency module 140 can have the passive elements 153 to 155 formed in the element forming layer 142 with a high precision. Also, since the base substrate block 141 and element forming layer 142 are electrically isolated from each other to improve the performance and assure a power circuit etc. having a sufficiently large area, so the high-frequency module 140 can be supplied with a high-regulation power.
Also, in the high-frequency module 140 shown in FIG. 5, the passive elements 153 to 155 formed in the element forming layer 142 are influenced by the ground pattern formed on the first wiring layer 147 at the base substrate block 141. In the high-frequency module 140, the inductor 154, for example, develops a capacitance between itself and the ground pattern to have a reduced self-resonant frequency and quality factor Q. In the high-frequency module 140, the passive elements 153 and 155 also vary or becomes worse in performance.
To solve the problems of the aforementioned conventional high-frequency module 140, there has been proposed another high-frequency module as shown in FIG. 6. The high-frequency module, generally indicated with a reference 160, has pattern openings 161a and 161b formed in the ground pattern on the first wiring layer 147 opposite to the passive elements 153 to 155 at the element forming layer 142. It should be noted that since the components of the high-frequency module 160 in FIG. 6 are the same as those in the high-frequency module 140 shown in FIG. 5, so they are indicated with the same references as those in FIG. 5 and will not be described in detail any longer. Thus, in the high-frequency module 160 shown in FIG. 6, the passive elements 153 to 155 will be influenced by the third wiring layer 149 via the organic substrate layer of the first organic substrate 143 and the prepreg 145, but they will be improved in performance.
In the high-frequency module 140 in FIG. 5 and the one 160 in FIG. 6, each of the organic materials of the first and second organic substrates 143 and 144 is a substrate material formed by integrating a woven glass fabric with each of the first and second organic substrates 143 and 144. Such a substrate material is formed by continuously supplying a woven glass fabric, generally rolled in the form of a roll, into a bath filled with an emulsified organic material, thus saturating the woven glass fabric with the organic material, adjusting the thickness of the organic material-saturated woven glass fabric, drying the woven glass fiber, and make some other process of the woven glass fabric to a desired thickness. Then, the first and second organic substrates 143 and 144 are formed by applying an adhesive to the top or bottom main side of the substrate material as a core, bonding a rolled copper foil having the surface thereof roughened to the substrate material and cutting the latter to a predetermined size.
In the high-frequency module 160 in FIG. 6, since each of the organic substrates is larger in specific inductive capacity than the woven glass fabric, the line pattern 152 of the distributed parameter circuit formed on the base substrate block 141 is influenced in both conductor loss and inductive loss by the woven glass fabric in the aforementioned first and second organic substrates 143 and 144, and thus has the performance thereof degraded. Also, in the high-frequency module 160 in FIG. 6, in case the glass fibers are woven with a large pitch, the line pattern 152 will be formed over a portion where the glass fibers are laid and a portion where no glass fibers exist are laid. In the high-frequency module 160 in FIG. 6, the effective specific inductive capacity and dielectric dissipation factor (Tan δ) “vary” in the first and second organic substrates 143 and 144 depending upon whether or not the glass fibers are laid. The “variation” of the effective specific inductive capacity is found large where the glass fibers are laid thick, and small where the glass fibers are laid thin. Namely, the effective specific inductive capacity varies periodically (with the pitch of the glass fibers) in a range of a difference between the maximum and minimum values.
The high-frequency module 160 shown in FIG. 6 is lower in reliability and yield in some cases because of the degraded performance, larger “variation” and difficult reproducibility of the line pattern 152. Thus, the high-frequency module 160 will be higher in cost because it has to be adjusted after produced. Also, in case the high-frequency module 160 has other lines and various passive elements formed in the base substrate block 141 thereof with the thin film technology in addition to the line pattern 152, the same problems will possibly take place due to increases or “variations” of effective specific inductive capacity and dielectric dissipation factor (Tan δ) under the influence of the glass fibers used to form the organic substrates.